I. Field of the Invention
The present invention relates to a cryostat and, more particularly, to a cryostat formed of a fiber-glass reinforced plastic.
II. Description of the Prior Art
A cryostat is used when cryogenic fluid, e.g., liquid helium used for cooling a superconducting device, liquid nitrogen, liquid oxygen, or liquefied natural gas used for the other utilities, is stored and transported. The cryostat should be formed of a material which can endure the temperature (4.2.degree. K for the liquid helium) of such a cryogenic fluid.
Metallic materials and organic materials generally tend to increase their tensile strength in the vinicity of the cryogenic temperature. At the same time, however, they are brittle and their elongation is reduced. Since general organic materials in particular has heat transfer coefficients ten to hundred times lower than those of metallic material, they have relatively low heat losses due to heat conduction. They are accordingly considered to be adequate for storing cryogenic fluid. However, the material should be considerably thicker than the metal so as to provide a structure having a predeterminded tensile strength.
The conventional cryostats have been composed of metallic materials, e.g., stainless steel, at the cost of heat loss characteristic of the metallic materials. When a cryogenic device e.g., a superconducting pulse magnet (used for a troidal coil for a nuclear fusion reactor) producing change with time of a magnetic field is operated in a metallic cryostat, an eddy current will flow due to its electromagnetic induction in the metallic cryostat, and cryogenic fluid, e.g., liquid helium contained in the cryostat, is disadvantageously evaporated due to the Joule's heat of the eddy current. This is the result of the electric conductivity of the metal.